This is a deductively valid argument, which is to say if its premises are true its conclusion cannot be false. The key question is whether or not the premises are true.

The first premise is by far the most often-disputed premise in the argument. While many religious believers take the first premise for granted, the reasons for thinking it true are not clear, and there are some serious objections to it.

Arguments for the first premise

Famous atheists rejected morality

Though this line of argumentation is popular among religious apologists, it clearly commits the fallacy of appealing to authority, and that is not its only problem. Many nontheists who have rejected conventional views of morality have done so on grounds independent of their views on the existence of God. Also, it requires selectively quoting authorities, because many nontheists--indeed, many theists--have rejected the first premise of the moral argument. Finally, it is trivially easy to construct a similar argument against theism, for example: "John Calvin did not believe in free will, therefore 'If God exists, free will does not exist,' but free will does exist, therefore God does not exist." Even if Calvin had good arguments for his stance on free will being entailed by theism, non-Calvinistic theists will not be swayed by the mere citation of Calvin's authority, nor should they be.

Hitler and Stalin were atheists

The basic fallacy of this argument is similar to the one in the first, though it could be considered an example of guilt by association rather than an appeal to authority. Furthermore, the historical accuracy of the argument can be questioned. Hitler's theistic proclaimations are well documented,[1] and anti-religious quotes attributed to him are apparently inauthentic. He seems to have held to basic doctrines of Christianity, in spite of rather unorthodox changes, such as his belief that Jesus was an Aryan and Paul corrupted Christianity with proto-Bolshevism. Stalin was an atheist, but given that this is one of many beliefs he held, it is unclear why his actions should be attributed to his atheism. For example, though many would be surprised by this, Stalin opposed mainstream theories of evolution on the grounds that they were too capitalistic. Stalin's rejection of evolution could just as easily be named the source of his crimes as his rejection of God, and indeed his rejection of evolution arguably sheds more light on the ideological dogmatism at the heart of the Soviet regime.

If God does not exist, humans are just animals

One snappy response to this argument is "Humans are animals whether or not God exists," which has indeed been the consensus view among taxonomists since Aristotle. Though this point may seem trivial, but beneath it is the deeper point that it is hard to see how God's existing or not existing changes the status of humans. If the theist insists on claiming that human beings are worthless on their innate attributes alone, it is hard to see how God could change this situation.

Moral law requires a Lawgiver

Though we sometimes use the same words to talk about moral principles and human legislation, closer inspection calls into doubt the claim that there is a strong analogy between them. Human laws can be changed if the government wills it and follows correct procedures, but moral principles are typically thought to be unchanging. Also, it is possible to have a bad human law, but it is impossible to have a bad moral principle. In response to this second argument, it could be claimed that amoral laws are analogous to acts of a lower body that violate acts of a higher body which the lower body is responsible. This seems intuitively wrong, however: the wrong in a national law relegating part of the population to sub-human status seems very different, and more serious, than the wrong in a local law that contradicts a state

God's rewards and punishments needed to make morality in one's own self interest

Usually, this argument is not stated so baldly. A more typical statement is "we admire people who sacrifice their lives for others, but if there is no God who rewards self-sacrifice, then such people are being stupid." When the underlying assumption is stated explicitly, most people recoil. Most people do not believe that the ultimate maxim by which we should act is "look out only for your own self interest." Though such a view is technically an ethical theory (known to philosophers as ethical egoism), it is not what most people mean when they talk about morality. It seems that if ethical egoism is true, then the second premise of the moral argument is false, at least in the normally understood sense.

Absolute morality requires an absolute standard

Statements of this argument are often unclear, but it seems to rest on an equivocation of the term "absolute," in much the same way that the Lawgiver argument rests on an equivocation of the term "law." The two relevant senses here are "applicable in all cases" (a characteristic typically applied to moral principles) and "omnipotent, omniscient, etc." (a characteristic typically assigned to God). There is no reason to think that the first sense entails the second sense.

Arguments against the first premise

The Euthyphro dilemma

This is perhaps the most famous objection to the second premise. The Euthyphro dilemma is found in Plato's Euthyphro, in which Socrates asks the question, "Is the pious loved by the gods because it is pious, or is it pious because it is loved by the gods?" In layman's terms this would be, "Is that which is good commanded by God because it's good, or is it good because God commands it?" Both options are problematic for those who would claim morality is dependent upon God.

If God is free to decide what is good, and it is good by virtue of his decree, then God has no higher standard to answer to. Therefore his will may be seen as genuinely arbitrary. Although God once decreed that murder and theft are morally wrong, he might have declared the opposite just as easily, so then murder and theft would be right. This makes morality arbitrary, not what most theists mean to say in articulating the second premise of the moral argument.

If right and wrong are inherent to the action, regardless of God's decree, then God has nothing to do with the process. God doesn't set moral standards; he follows them, and is therefore irrelevant to morality (except to the extent that he can tell us things which we could not figure out for ourselves.)

"The point I am concerned with is that, if you are quite sure there is a difference between right and wrong, then you are then in this situation: is that difference due to God's fiat or is it not? If it is due to God's fiat, then for God himself there is no difference between right and wrong, and it is no longer a significant statement to say that God is good."

One perceived way to get out of the dilemma is to say that, although God has the freedom to command immoral acts such as rape, he would never do such a thing because it goes against his character or nature.

In response, Michael Martin has argued that this doesn't solve anything because the dilemma can be reformulated in terms of God's character: "Is God's character the way it is because it is good or is God's character good simply because it is God's character?"[2] The structure of this modified dilemma is exactly the same as before, and it appears to be if anything harder to escape.

Moral truths as necessary truths

Richard Swinburne, a theistic philosopher, has argued that moral truths cannot depend on God because moral truths are necessary truths, existing in all possible worlds, including ones where God does not exist. This objection of Swinburne's was cited by Jeffery Jay Lowder in Lowder's debate with Phil Fernandes.[3] Keith Yandell, another theistic philosopher, raised a similar objection in his comments on the Craig-Flew debate.

Secular morality

Finally, it can in general be claimed that there is a specific, well-founded theory of morality that leaves God out of the picture. This is a complex topic and is dealt with in full by the above-linked article. One thing is worth noting here: some theists appear to think that it constitutes a valid link in the moral argument to simply demand a secular theory of morality without giving any reason to think that theistic theories are more likely to be sucessful. This is clearly fallacious, and debaters should not fall into this trap. Meta-ethics, like most areas of philosophy, has unresolved debates, but pointing to an unresolved philosophical debate is no argument for the exstience of God. To show that the moral argument is unsuccessful, one need only show that we should not accept the second premise. Full development of secular theory of morality may be helpful here, but it is not necessary.

Other formulations of the moral argument

Normativity of morality

This formulation of the moral argument relies on the assumption of normativity, that is to say, that the awareness of morality is a more or less universal experience among humans. Most people recognize that, for example, murder is wrong. From there, a theist claims that this universal awareness must come from some ultimate source, which is God.

To put it concisely:

It appears to human beings that moral normativity exists.

The best explanation of moral normativity is that it is grounded in God.

Therefore God exists.

This version of the moral argument may sometimes be used by theists as red herring when responding to arguments about the moral nature of God. For instance, a person who points out the inherent cruelty of exterminating 99% of the earth's population, as in the story of Noah's ark, or takes issue with the apparent Biblical support of slavery and rape, may quickly expect to be countered with this claim:

"You recognize mass murder/slavery/rape as a bad thing, so you must have some standard to judge that against. If there was no God, then you'd have no rational reason to say that those things aren't good."

Counter-apologetic responses to normativity

Although the awareness of SOME sort of right and wrong is apparently universal, many specific details differ across cultures and time periods. In the case of slavery, for example, the practice was once universally accepted in the southern United States, and many anti-abolitionists even quoted the Bible to justify the practice. (See the main slavery article for more details.) This indicates that morality has a strong cultural component to it, and is tied up in evolving notions of secular morality.

Other human perceptions also have the appearance of being normative. For instance, most people agree that chocolate is "delicious," while dirt is "not delicious." By the same reasoning as the argument from normative morality, it could be said that there must be some ultimate standard for deliciousness, and that standard must be God, the ultimate tasty treat. We could use a similar argument to prove that God is the definition of the perfect homosexual lover.

The fact that there may be an abstract standard of perfect goodness that an individual strives to achieve, does not indicate that this standard represents an existing object. For example, bowling a perfect game would yield a score of 300. However, even if no one in history had ever bowled a 300, this would still be the highest attainable score according to the rules of the game. It is quite possible to have a theoretical ideal, yet not have any concrete instance of that ideal. Therefore, we could say: "Yes, this thing that you call 'God' could be our standard for morality. However, this tells us nothing about whether or not God exists."